The field of the invention relates to control systems for maintaining engine air/fuel operation within the peak efficiency window of a catalytic converter. A particular aspect of the field relates to adaptively learning a correction value for the exhaust gas oxygen sensor output so that the output will coincide with the converter's peak efficiency window.
Air/fuel ratio feedback control systems responsive to exhaust gas oxygen sensor outputs are well-known. Conventional sensors are used which have two saturated output voltage states dependent upon presence or absence of sufficient free oxygen in the exhaust gases. Typically, the sensor output is compared to a reference selected at the approximate midpoint in the saturated output voltage states. A two-state signal is thereby derived indicating when engine air/fuel operation is either rich or lean of stoichiometric combustion.
The inventors herein have recognized several problems with the above approach. The step change of the two-state signal may not occur at the converter's peak efficiency window. Although the inventors herein have recognized that the step change may be shifted towards the window by pumping current through a sensor electrode, such current pumping may cause a shift in amplitude of the sensor output. Consequently, the reference may no longer coincide with the midpoint of the saturated output voltage states.